Fuel cell power systems have been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One type of fuel cell power system employs use of a proton exchange membrane (PEM) to catalytically facilitate reaction of fuels (such as hydrogen) and oxidants (such as air or oxygen) into electricity. Typically, the fuel cell power system has more than one fuel cell that includes an anode and a cathode with the PEM therebetween. The anode receives the hydrogen gas and the cathode receives the oxygen. The hydrogen gas is ionized in the anode to generate free hydrogen ions and electrons. The hydrogen ions pass through the electrolyte to the cathode. The hydrogen ions react with the oxygen and the electrons in the cathode to generate water as a byproduct. The electrons from the anode cannot pass through the PEM, and are instead directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle. Many fuel cells are combined in a fuel cell stack to generate the desired power.
The fuel cell power system can include a high pressure vessel or container for storing hydrogen gas for the fuel cell stack. The high pressure vessel can be charged with hydrogen gas at a filling station and the like. The hydrogen gas is transferred from the filling station to the high-pressure vessel on the vehicle to supply the hydrogen gas to the fuel cell stack as needed.
High-pressure vessels generally require high pressure shutoff valves for serviceability and to minimize hydrogen gas release to the ambient atmosphere. Typically, the shutoff valves are electrically-operated solenoid valves. The sealing of common solenoid valves is typically realized by an O-ring, which is generally mounted on a main piston inside the valve body. The solenoid valve is activated by a power source to produce a magnetic force. The magnetic force of the solenoid works against a metal coil spring disposed inside of the valve body to open the valve. The spring otherwise biases the main piston in a closed position.
When the piston is displaced by either the spring or the solenoid, there is a relative movement and a friction between the O-ring and the valve body. The level of friction depends on many parameters such as temperature, lubrication, harshness, number of cycles, age of O-ring, abrasion, etc. If the friction is too high, the piston can undesirably “stick” in the open position. Conventional electrically-operated solenoid valves are therefore known to having issues with controllability due to the friction between the O-ring and the valve body. The piston and O-ring seal also require lubrication in order to avoid the sticking and maintain the controllability of the shutoff valve.
There is a continuing need for a high pressure tank valve that minimizes friction at a piston of the high pressure tank valve, eliminates the need for lubrication of the O-ring seal, and which is optimized for manufacturability.